1. Field of the Invention
This invention relates generally to an optical inverter and, more specifically, to an optical inverter that incorporates a saturable absorber that receives an optical input signal to switch the absorber from an opaque mode to a transparent mode to distinguish between a logical one and a logical zero output.
2. Discussion of the Related Art
The art of digital logic systems consistently requires the need for greater processing speeds, increased channel bandwidths, and improved transmission reliability for information processing and transmission fields. Because of this continued need for improved system performance, the art is moving towards an increased focus on the optical domain. Digital logic systems typically incorporate a plurality of inverters. Inverters are important in digital systems for many reasons, such as the application of DeMorgan's theorem. DeMorgan's theorem allows the combination of only AND gates and inverters, or a combination of only OR gates and inverters, to form a complete gate set. Also, optical inverters are a vital component of optical analog-to-digital converters. An optical analog-to-digital converter is disclosed in U.S. patent application Ser. No. (Attorney Docket No. 12-0854), assigned to the assignee of this application.
Various types of optical inverters are known in the art. One optical inverter known in the art is referred to as a semiconductor optical amplifier (SOA) inverter. The SOA inverter is a saturable optical amplifier that includes a first optical input having a first wavelength, a second optical input having a second wavelength and an optical output that is a combination of the first and second inputs. The first input goes high and low as a digital high and a digital low, and the output conversely goes low and high as an inversion of the first input. The second input is maintained high. When the first input is low or zero, the output is simply the second input, thus representing a high or logical one. When the first input goes high, the intensity of this first input is great enough to saturate the SOA. As a result the amount of light intensity in the output from the second input is reduced. The output beam is then passed through a filter which removes the wavelength of the first input, leaving only the second input. This filtered output will then appear to go down when the first input goes high and come back up again when the first input goes low.
Because the main use of the SOA is a wavelength conversion device for use in wavelength division multiplexing technology, it is limited in its ability to be used as an inverter. Further, the SOA is an active device that is fairly complex and is generally not efficient as an optical inverter. What is needed is an optical inverter that is simptler and more effective than those optical inverters known in the art It is therefore an object of the present invention to provide such an inverter.